This invention relates to light emitting devices comprising a light emitting diode or laser diode (LED), an excitable phosphor, and a scattering medium for providing uniform light illumination. It finds particular application in combination with a UV/Blue LED and a phosphor or blend of phosphors, for converting LED-generated ultraviolet (UV) and/or blue light into white light for general illumination purposes. It should be appreciated, however, that the invention is also applicable to the conversion of light from other LED sources to light of a different wavelength.
The advent of GaN-based epitaxial structures has lead to the development of UV and/or blue (xe2x80x9cUV/bluexe2x80x9d) light emitting devices, including light emitting diodes and lasers (generally referred to herein as LEDs). By combination of the light emitting device with one or more phosphors, generation of visible light (e.g., red, blue, or white light) is achieved. The phosphor transforms a portion of the UV or blue light into light of longer wavelength, for example, by employing a UV/blue absorbing, yellow emitting phosphor, such as Y3Al5O12-Ce3+ (commonly referred to as YAG-Ce), obtainable from Nichia Chemical Company.
The YAG-Ce phosphor converts LED blue light into yellow light. This produces a white field with a color rendering index (CRI) of about 77 and a color temperature ranging from about 6000 K to 8000 K. For some applications, conversion of UV/blue light from an LED to visible light using phosphors may be more attractive than the direct application of visible LEDs. Such UV/blue LED phosphor devices, for example, offer the opportunity to encompass a wider color range, which is important for display as well as for illumination applications.
White LEDs, i.e., LEDs which employ a combination of a UV/blue LED with one or more phosphors to provide an approximate white color, suffer from one drawback. While the light which has been down-converted to yellow by the phosphor has a relatively uniform angular distribution, the blue, unconverted light is distributed in a non-Lambertian fashion. Thus, when the yellow light and blue light are combined to make white light, the light emitted is not a uniform white light over all forward angles (i.e., the light does not have a uniform emission strength when viewed at different angles).
While phosphors do have the effect of scattering both the unconverted and the converted light to some extent, phosphor materials also absorb light. Thus, it is not practical to use a phosphor material to provide Lambertian light distribution, since at the thickness which would be employed to provide an approximately uniform distribution, the absorbance of light by the phosphor would result in a substantial loss in the overall intensity of the light source.
The present invention provides a new and improved light source, which overcomes the above-referenced problems and others.
In an exemplary embodiment of the present invention, a light source is provided. The light source includes a light emitting component, which emits light, and a light scattering material, positioned to receive the light emitted by the light emitting component. The light scattering material scatters at least a first portion of the light, to improve an angular distribution of the light. A phosphor material is positioned to receive at least a second portion the light emitted by the light emitting component, the phosphor material converting the second portion of the light to light of a different wavelength.
In another exemplary embodiment of the present invention, a light source with improved angular light distribution is provided. The light source includes a light emitting component and a light scattering material, which receives light emitted by the light emitting component and scatters the light without appreciable absorption of the light. A phosphor material receives at least one of the light emitted by the light emitting component and the light scattered by the light scattering material. The phosphor material converts at least a portion of the received light to light of a different wavelength.
In another exemplary embodiment of the present invention, a method of producing light having a more uniform angular color distribution is provided. The method includes scattering light emitted by a light emitting component with a light scattering material to increase the uniformity of the angular distribution of the light; and converting at least a portion of the light emitted by the light emitting component to light of a different wavelength with a phosphor.
One advantage of the present invention is that UV/blue light is converted to white light with a relatively Lambertian distribution.
Another advantage of the present invention is that light is produced with a relatively uniform color over a wide range of viewing angles.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.